Identity ASP.NET MVC getting error when changing the AspNetUsers table

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C#

ASP.NET

MVC

C#5.0

Identity

During the whole day I just tried to add a single property to my AspNetUsers table generated by identity. I wanted that property to be a foreign key to a "Clients" table so that each client has it's own user and all the data of the client is in that respective clients table.
So here is what I've done:
In the IdentityModels:

public class ApplicationUser : IdentityUser
    {
        [ForeignKey("Client")]
        [DatabaseGenerated(DatabaseGeneratedOption.None)]
        public int ClientID { get; set; }
        public virtual Client Client { get; set; }
        public async Task<ClaimsIdentity> GenerateUserIdentityAsync(UserManager<ApplicationUser> manager)
        {
            // Tenga en cuenta que el valor de authenticationType debe coincidir con el definido en CookieAuthenticationOptions.AuthenticationType
            var userIdentity = await manager.CreateIdentityAsync(this, DefaultAuthenticationTypes.ApplicationCookie);
            // Agregar reclamaciones de usuario personalizado aquí
            return userIdentity;
        }
    }

And in the AccountController

public async Task<ActionResult> Register(RegisterViewModel model)
        {
            if (ModelState.IsValid)
            {
                //Para crear el cliente y el contexto
                var currentClient = new Client { Email = model.Email, Name = model.Name, Surname = model.Surname, PhoneNumber = model.PhoneNumber };
                var context = new TNEAContext();
                context.Clients.Add(currentClient);
                context.SaveChanges();

                //Esto ya venia con el codigo
                var user = new ApplicationUser { UserName = model.Email, Email = model.Email, ClientID = currentClient.ClientID };
                var result = await UserManager.CreateAsync(user, model.Password);
                if (result.Succeeded)
                {
                    await SignInManager.SignInAsync(user, isPersistent:false, rememberBrowser:false);
                    
                    // Para obtener más información sobre cómo habilitar la confirmación de cuenta y el restablecimiento de contraseña, visite http://go.microsoft.com/fwlink/?LinkID=320771
                    // Enviar correo electrónico con este vínculo
                    // string code = await UserManager.GenerateEmailConfirmationTokenAsync(user.Id);
                    // var callbackUrl = Url.Action("ConfirmEmail", "Account", new { userId = user.Id, code = code }, protocol: Request.Url.Scheme);
                    // await UserManager.SendEmailAsync(user.Id, "Confirmar cuenta", "Para confirmar la cuenta, haga clic <a href=\"" + callbackUrl + "\">aquí</a>");

                    return RedirectToAction("Index", "Home");
                }
                AddErrors(result);
            }

            // Si llegamos a este punto, es que se ha producido un error y volvemos a mostrar el formulario
            return View(model);
        }

And some other minor changes in the accountViewModel and the register view (in order to get those params).

I know that my problem is on the UserManager.CreateAsync method, but I don't know how to modify it, or what do I need to do in order to do that little change that is driving me mad :(